The present invention relates to a filter element, in particular for filtering liquids or gases, e.g., for filtering oil for an internal combustion engine, having a bypass valve for the fluid to be filtered. Furthermore, the invention relates to a filter device suitable for containing the filter element of the invention, and to a method for maintaining a filter device of the invention.
It is known that in fluid filters having cylindrical filter inserts the bypass valve can be accommodated in the area of an end disk. The bypass valve is provided on the filter element to ensure fluid flow in the case of an unacceptable increase in flow resistance such as a clogged filter. By opening the bypass valve, the supply of fluid or gases to the system is ensured in this case.
A fluid filter with a bypass valve is disclosed, for example, in U.S. Pat. No. 5,770,054 (=DE 196 05 425). FIG. 2 in that document shows a fluid filter in a disassembled state. A supporting dome is provided in the housing, to which is attached a valve body biased by a spring. This valve body finds a valve seat in the end disk belonging to the filter element when the filter element is installed. This provides an inexpensive design of the bypass valve. When the filter element is changed, however, only the valve seat together with the filter element is replaced. The valve body remains in the supporting dome, which is designed to be permanently attached to the housing. Therefore in the course of use of the filter, the valve body is subject to wear and soiling. With modern diesel engines in particular, the valve body may lose its tightness due to deposits of particles, so that an unwanted and unfiltered side stream of the lubricating oil is formed at the bypass valve. This worsens the quality of the lubricating oil, so that either the function of the internal combustion engine is endangered or more frequent oil change intervals are required. To avoid a malfunction, the valve body could also be replaced each time the filter is changed, but this creates increased installation costs and creates possible sources of error because the mechanic might forget to replace the valve body.